An atom of an element has 54 protons. Some of the elements atoms have 77 neutrons, while other atoms have 79 neutrons. What are the atomic numbers and mass numbers of the two types of atoms of this element?

The atomic numbers of both are 54 while the mass numbers are 131 and 133 respectively.

Explanation:

- The number of protons = Atomic number. So, if the atom has 54 protons and it remained unchanged, then the two types of atoms of this element both have atomic numbers of 54.

- On the other hand, mass number is the sum of protons and neutrons

So, if type 1 has protons = 54 and neutrons = 77: mass number = 54 + 77 = 131

if Type 2 has protons = 54 and neutrons = 79: mass number = 54 + 77 = 133

(Since the possibility of atoms of the same element to have different mass numbers but the same atomic number is called isotopy). The two types of atoms with mass numbers 131 and 133 described are isotopes.